std::num_get
| Defined in header <locale>
|
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| template< class CharT, |
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Class std::num_get encapsulates the rules for parsing string representations of numeric values. Specifically, types bool, unsigned short, unsigned int, long, unsigned long, long long, unsigned long long(since C++11), float, double, long double, and void* are supported. The standard formatting input operators (such as cin >> n;) use the std::num_get facet of the I/O stream's locale to parse the text representations of the numbers.
Inheritance diagram
If a std::num_get specialization is not guaranteed to be provided by the standard library (see below), the behaviors of its get() and do_get() are not guaranteed as specified.
Specializations
The standard library is guaranteed to provide the following specializations (they are required to be implemented by any locale object):
| Defined in header
<locale> | |
| std::num_get<char> | creates narrow string parsing of numbers |
| std::num_get<wchar_t> | creates wide string parsing of numbers |
In addition, the standard library is also guaranteed to provide every specialization that satisfies the following type requirements:
-
CharTis one of- char,
- wchar_t, and
- any other implementation-defined character container type that meets the requirements for a character on which any of the iostream components can be instantiated; and
-
InputItmust meet the requirements of LegacyInputIterator.
Member types
| Member type | Definition |
char_type
|
CharT
|
iter_type
|
InputIt
|
Member functions
constructs a new num_get facet (public member function) | |
invokes do_get (public member function) |
Member objects
| static std::locale::id id |
id of the locale (public member object) |
Protected member functions
destructs a num_get facet (protected member function) | |
| [virtual] |
parses a number from an input stream (virtual protected member function) |
Example
#include <iostream> #include <iterator> #include <locale> #include <sstream> #include <string> int main() { std::string de_double = "1.234.567,89"; std::string us_double = "1,234,567.89"; // parse using streams std::istringstream de_in(de_double); de_in.imbue(std::locale("de_DE.UTF-8")); double f1; de_in >> f1; std::istringstream us_in(de_double); us_in.imbue(std::locale("en_US.UTF-8")); double f2; us_in >> f2; std::cout << "Parsing " << de_double << " as double gives " << std::fixed << f1 << " in de_DE locale and " << f2 << " in en_US\n"; // use the facet directly std::istringstream s3(us_double); s3.imbue(std::locale("en_US.UTF-8")); auto& f = std::use_facet<std::num_get<char>>(s3.getloc()); std::istreambuf_iterator<char> beg(s3), end; double f3; std::ios::iostate err; f.get(beg, end, s3, err, f3); std::cout << "parsing " << us_double << " as double using raw en_US facet gives " << f3 << '\n'; }
Output:
Parsing 1.234.567,89 as double gives 1234567.890000 in de_DE locale and 1.234000 in en_US parsing 1,234,567.89 as double using raw en_US facet gives 1234567.890000
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 427 | C++98 | num_get was guaranteed to accept any CharT thatmeets the requirements for a character on which any of the iostream components can be instantiated |
only guarantees to accept char, wchar_t and other implementation- defined character types |
| LWG 2392 | C++98 | only character type CharT could beguaranteed to be accepted by num_get
|
can guarantee to accept implementation- defined character container types |
See also
| defines numeric punctuation rules (class template) | |
| formats numeric values for output as character sequence (class template) | |
| extracts formatted data (public member function of std::basic_istream<CharT,Traits>) |